The reaction nC2H4 + (-C2H4-)n is an
example of
1.
saponification
2.
esterification
3.
polymerization
4.
fermentation

Polymerization

Explanation:

Polymerization is the process by which molecules of small organic compounds combine repeatedly, in a regular manner, to form a complex organic compound. These small organic repeated units are called monomers, while the complex product formed are referred to as polymer.

In this reaction,

nC₂H₄ + -(C₂H₄-)n is the combination of smaller units of C₂H₄(ethene) to form larger units of (C₂H₄)n (polyethene).

Polyethene is formed due to addition polymerization which is the process where ethene break their double bonds to form links, so that the empirical formula of both are the same. This occurs in a chain reaction and the process is known as polymerization.